Almost simultaneously three batteries of Archies opened fire, and soon the biplanes were rocking, lurching, and side-slipping in the air-eddies caused by the bursting shrapnel. It was now the battleplanes' opportunity. Leaving two of their number to wireless the news that the enemy trench was no longer held, the remainder dived steeply at the troublesome anti-air-craft batteries. Although one British machine was shot down completely out of control, the remainder attained their objectives. With bombs of terrific explosive power they wiped the Archies out of existence, and then proceeded to drop more bombs upon the dug-outs in order to induce Fritz to bolt from his lair. Meanwhile the British infantry were advancing in open order with fixed bayonets and preceded by bombers. Viewed from aloft, the movement lacked vigour. A battle photograph, taken from an aeroplane, is a very tame picture compared with the results obtained by daring cinematographers, who frequently film the process of "going over the top". The absence of sound--or rather the drowning of it by the roar of the engine--the grotesque foreshortening of the figures, and their relatively slow rate of progress all fail to convey any picturesque aspect of a modern battle when observed from a machine flying high overhead. Derek was describing a series of circles, ready to traverse the line of trenches at an instant's notice, when he saw a sight that bore testimony to the stubborn nature of the Prussian infantryman. It was not without a set purpose that the German High Command had manned this sector with picked troops. Apparently the underground works were of a very extensive nature, and concealed not only the troops presumably in the trench, but very stiff reserves as well. At a signal, the Prussians issued in swarms from their subterranean retreats. Along the parapet flashed a crackling line of fire, as machine-guns by scores and hundreds of rifles loosed their leaden hail upon the advancing khaki troops. No living creature could last for long in that fire-swept zone. The ground was dotted with dead and wounded, many of the latter still using their rifles against their foes. Individual courage was of no avail against the diabolical scientific devices of the Huns, who used petrol-bomb, flame-thrower, and poison-gas with horrible effect. Stolidly the khaki-clad infantry retired to their former positions. Here, on the defensive, and with their backs to the broad canal, they must wait and sit tight until heavy artillery and tanks turned the scale of battle. It was a chance for the airmen. Up and down, often at less than twenty feet above the densely-packed German lines, they flew, their machine-guns cutting broad swaths in the field-grey masses. Often hidden in clouds of smoke, risking collision with other British machines, the biplanes soared and swooped until red-hot guns and empty ammunition-trays called a halt.